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From: At my Bar drinking and wrenching in Lafayette Colorado
Unfortunately, Holley does not publish their air bleed sizes for most of their carbs - you have to call the Holley Tech line to get that data. The .045 diameter for the low speed bleed on the primary side of a spread bore sounds about right. If it's too small, you'll have an overly-rich cruise condition, and your idle mixture screws will be at 1/2 turn or less. If you compare the 4175 setup to a similar-sized 4150, you'll see no similarities between the two: the 4175 with the small primaries and huge secondaries has a very unique setup unlike any other Holley spec (650 4150 mechanical secondary carbs usually have low speed bleeds up around .059). It's unlikely that someone would extract the low speed bleeds and install undersized bleeds - it's more common to see them drilled out.
All that said, the primary low speed air bleeds on a 6210-3 (4165 650 cfm spreadbore) are .057. So your hunch that .045 is a little small could be correct...If you're seeing a rich idle, transition and cruise condition, you're probably on the right track.
Lars
Thanks Lars that is exactly what I am seeing rich idle and rich low speed cruise. I have opened them up to .052 right now ( only bit close I have)which matches the secondary side and will test again . Thanks
From: At my Bar drinking and wrenching in Lafayette Colorado
It doesn't take much of a change in low speed air bleed diameter to make a pretty significant change in mixture, so starting with the .052 is probably a good idea. Drill size #54 is .055, and #53 is .059, which should be your next progression steps if the .052 doesn't do the trick...
The other thing you can do is take a plain office staple out of your stapler, straighten the one bend to shape the staple into an "L", and then insert the short leg of the staple into the idle fuel restrictor orifice in the metering block. Sandwich the long leg of the stable under the metering block gasket to retain it. This will also have a lean-out effect on the idle, transition, and light cruise mixtures, and it's not as permanent as the drilling operation on the air bleeds.
Here is where you can put the staples Lars suggested. Copper wire strand works too. Put one on each side.
Here is something else to check. Idle transfer slot setting is changed with the idle speed screw. Set the screw so the slot is barely exposed and looks like a "square". If you still need more air (RPM) at idle, you can crack the secondary stop screw to allow more air.
From: At my Bar drinking and wrenching in Lafayette Colorado
For the IFR restriction, I like to use a plain staple out of an office stapler because these common office staples are very thin - they are only .019" diameter, which tends to be just the right amount of additional IFR restriction if there is a rich-running problem. Also note that the IFR orifice can be located either up high or down low in the metering block, depending on the metering block design, referred to as "idle jet" in this illustration:
Lars
First and foremost be sure those air bleeds are not plugged up. Spraying with carb cleaner you need to watch the patterns out each bleed hole. Any diff from one side to the other is an obstruction. The holes themselves plug up and take finding the right size and stiffness of wire to unclog. New metering blocks may be easier if you find them plugged.
